Surface-treating fluoropolymer powders using atmospheric plasma

ABSTRACT

Fluoropolymer powder particles which are surface treated so as to change the chemical functionality on their surfaces which in turn changes the surfaces characteristics. These characteristics improve the usefulness of these powders and can make them wettable. The surface treated fluoropolymer particles are subject to an atmospheric plasma treatment process, and preferably pretreated with a macromolecular chemical species prior to the atmospheric plasma treatment. The atmospheric plasma treatment enhances adhesion to the powder surface and can also enhance cross-linking of the macromolecular chemical species. The surface treated fluoropolymer powders can be used to form fluoropolymer coatings on various substrates.

TECHNICAL FIELD

[0001] The present invention relates to fluoropolymer powders. Moreparticularly, the present invention is directed at producing a novelfluoropolymer powder by immobilizing macromolecules on the surface ofthese powders using atmospheric plasma and other techniques.

BACKGROUND ART

[0002] Fluoropolymers, are defined herein broadly as any of the fluorinecontaining polymers, including homopolymers, copolymers, and terpolymersthat have non-wettable and chemical inert surfaces which, although beingdesired in some applications, limit the use of these materials in otherapplications.

[0003] The technology of coating of articles with fluoropolymers hasbeen developing along two fundamentally distinctive directions based onthe physical form of powder and latex fluoropolymers. In each case, thefinal coating (a continuous film layer) is obtained by heating theapplied fluoropolymers above their melting.

[0004] Processes and products have been developed which provide specificadvantages for powder and latex fluoropolymer applications. Fortechnologies that use powdered fluoropolymers, modified polymercompositions and particle sizes and shapes have been developed toadvance both the application yield (yield per pass) and the performanceof the resulting film per unit film thickness. The major intrinsicobstacle to advancements in the use of powdered fluoropolymers is theirpoor electrical surface conductivity.

[0005] For latexes, the ultra low surface energy and the high specificgravity peculiar to fluoropolymers (they can be defined as being fullyhydrophobic) has forced the adoption of different manufacturingtechnologies since the base polymer synthesis (e.g. dispersion) ischaracterized by polymer particles having an average diameter two ordersof magnitude smaller then powders, and by the extensive use ofsurfactants, both the fluorinated surfactants used during synthesis, andhydrogenated surfactants for the creaming of diluted dispersion obtainedfrom the synthesis, and for the stabilization and formulation ofconcentrated latexes manageable by the application techniques (e.g.spray, roll, curtain coating). However, both kinds of surfactants,intrinsic to the technology, are detrimental to the coating application,negatively impacting the yield and the characteristics of the film layer(e.g. film continuity, adhesion to the substrate, etc.).

[0006] A way to escape from these two fundamental approaches istheoretically conceivable, and involves the modification of thefluoropolymer particle surface, to make it more compatible with thebroad spectrum of available polar carrier means (e.g. water), butwithout altering/damaging the properties of the fluoropolymer bulk.

[0007] Surface treatments of fluoropolymer are known and established inthe art. Fluoropolymers in the form of sheets, films and shaped articleshave been chemically treated, subject to electrical discharged usingcorona discharge and plasmas, subject to flame treatment, and subject tophysical treatment such as chemical adsorbing procedures. In eachinstance, desired results have often been less than satisfactory. Forexample, surface changes effected by chemical treatments producesdarkening of the surface and chemical absorbing procedures are subjectto deterioration and loss over time.

[0008] Flame treatments can cause undesired damage if not properlycontrolled.

[0009] Electrical treatments seem to have become the most acceptedprocesses for desired long term effects. However, as discussed below,these treatment processes have limitations.

[0010] Corona discharge and flame treatment processes are used fortreating the surfaces of polymer films and other substrates such asfoils, papers, etc. These treatment processes increase the surfaceenergy of the substrates, which in turn improves the wettability,printability and adhesion on these surfaces. Corona discharges canproduce locally concentrated discharges known as streamers. Thesestreamers lead to some non-uniformity in the treatment of the filmsurfaces, and the concentrated energy of the streamers can alsomicroscopically damage the film surface. Furthermore, corona treatmentcan produce backside treatment, which is undesirable in manyapplications.

[0011] Flame treatment also has limitations in terms of oxidationsurface modification, difficulty in control and possibility of excessivethermal loads.

[0012] Plasma treatment is an effective method for treating surfaces toincrease surface energy and improve wettability, printability andadhesion. Plasma produces uniform surface treatment without causingbackside treatment of the substrate.

[0013] Low-pressure or atmospheric plasma treatment (APT) processes havebeen developed that provide unique advantages over existing technologiesfor surface treatment. The apparatus used in atmospheric plasmatreatment does not require a vacuum system, produces a high-densityplasma and provides treatment of various substrates at low temperaturewhile operating at atmospheric pressure. The benefits of plasmatreatment include reduced degradation of surface morphology, highertreatment (dyne) levels, elimination of backside treatment, and extendedlife over treatment time.

[0014] As reported by A. Yializis et al. (Atmospheric Plasma—The NewFunctional Treatment for Film, 2000 TAPPI Polymers, Laminations, &Coatings Conference pp. 1343-1352), atmospheric plasma treatmentprocesses have been developed for treating continuous webs and films.

DISCLOSURE OF THE INVENTION

[0015] According to various features, characteristics and embodiments ofthe present invention which will become apparent as the descriptionthereof proceeds, the present invention provides a surface treatedfluoropolymer powder which includes:

[0016] powder particles of a fluoropolymer; and

[0017] a coating of macromolecules on individual ones of said powderparticles.

[0018] The present invention further provides a method of providing awettable and reactive surface characteristic to fluoropolymer powderparticles which involves the steps of:

[0019] a) providing a fluoropolymer powder;

[0020] b) contacting the fluoropolymer powder with a macromolecularchemical species to coat particles of the fluoropolymer powder withmacromolecules; and

[0021] c) subjecting the coated particles from step b) to a process thatimmobilizes the macromolecules on the surface of the powder particles.

[0022] The present invention further provides a method of coating asubstrate with a fluoropolymer material which involves the steps of:

[0023] a) providing a fluoropolymer powder;

[0024] b) contacting the fluoropolymer powder with a macromolecularchemical species to coat particles of the fluoropolymer powder withmacromolecules;

[0025] c) subjecting the coated particles from step b) to a process thatimmobilizes the macromolecules on the surface of the powder particles;and

[0026] d) applying the surface treated particles to the surface of asubstrate.

[0027] According to different embodiments of the present invention, theprocess that is used to immobilize the macromolecules on the surface ofthe powder particles can be one of atmospheric plasma treatment, x-rayradiation, electron radiation, and ultraviolet radiation, and any otherprocess the effects cross-linking of the macromolecules.

[0028] The present invention also provides for a dispersion of thesurface treated fluoropolymer powder in a polar solvent, which can beused to produce various articles, compositions and additives.

BRIEF DESCRIPTION OF DRAWINGS

[0029] The present invention will be described with reference to theattached drawing, which is given as a non-limiting example only, inwhich:

[0030] FIG. 1 is a graph which shows weight loss versus number of passesthrough atmospheric plasma treatment for 5% PEG on PTFE.

BEST MODE FOR CARRYING OUT THE INVENTION

[0031] The present invention is directed to fluoropolymers, which asdefined herein includes any fluorine-containing polymer includinghomopolymers, copolymers and terpolymers, and fluoroelastomers. Examplesof fluoropolymers include:

[0032] 1. Homopolymers, including: polytetrafluoroethylene (PTFE),polytrifluoroethylene, polyvinylidene fluoride (PVDF),polychlorotrifluoroethylene (PCTFE), and polyvinyl fluoride (PVF);

[0033] 2. Co-polymers, including:tetrafluoroethylene-hexafluoropropylene know as fluorinatedethylene-propylene (FEP), tetrafluoroethylene and perfluorovinylethersknown as MFA and PFA, ethylene and tetrafluoroethylene known as ETFE,ethylene and chlorotrifluoroethylene known as ECTFE, vinylidene fluorideand hexafluoropropene known as fluoroelastomers; and

[0034] 3. Terpolymers, including:tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride known asTHV, vinylidene fluoride, hexafluoropropene and tetrafluoroethyleneknown as terpolymer fluoroelastomers.

[0035] Generally, these are polymers made with one or more of thefollowing specific examples of fluoromonomers including:tetrafluoroethylene, hexafluoropropylene, vinylidene fluoride, vinylfluoride, trifluoroethylene, chlorotrifluoroethylene, andperfluorovinylesters. Other non-fluoropolymers which are inert such aspolyether ether ketone (PEEK) and polyetherimide (PEI) can also betreated according to the present invention.

[0036] Fluoropolymers are well known as being inert and because of theirextremely low surface energy and non-polarity are non-wettable. Theirinertness makes fluoropolymers suitable for use in a variety ofapplications including bearing materials, non-stick cooking surfaces,etc. However, the inability to become wetted and their extreme chemicalinertness as a powder limits their application in other fields of use,in which they would seem to be otherwise very desirable. The surfacetreatment process of the present invention changes the surface chemistryof the fluoropolymer powder particles so the surface of the particlesare chemically reactive and interact with polar solvents, whilemaintaining the overall characteristics of the bulk fluoropolymerproperties.

[0037] During the course of the present invention, the inventordetermined to apply the most effective surface treatment technologiesthat are currently used to commercially treat fluoropolymer sheets,film, and other shaped articles to fluoropolymer particles. As a resultof these efforts, the present inventor unexpectedly discovered that allknown surface treatment technologies were not effective when applied tofluoropolymer powders.

[0038] According to the present invention, powders are defined as amaterial having a physical size of less than 100 microns, with no lengthto diameter restrictions or minimum particle diameter.

[0039] In attempting to apply atmospheric plasma treatment tofluoropolymer powders using existing techniques and technologies, it wasdiscovered that the high surface area of the powders prohibitedeffectiveness of the treatment even when atmospheric plasma treatmentwas carried out in the presence of reactive molecules in the gas phase.This is in contrast to the effectiveness of these techniques andtechnologies when they are used to treat PTFE sheet surfaces, whereindividual fluorine atoms are reacted and substituted by other smallchemical species to leave reactive groups on the sheet surface. It isbelieved that the difference results can be attributed to the fact thatthe unit surface area of a sheet or film of PTFE is very small ascompared to a powder which can have a surface area of 1 to 20 m²/g. Theinitial results of these tests indicate that existing techniques andtechnologies are uncompetitive for handling the high surface values offluoropolymer powders—residence time and power input would be far toogreat.

[0040] Accordingly, the present invention involves chemically treatingfluoropolymer powders prior to subjecting them to atmospheric plasmatreatment. The results of testing this treatment protocol demonstratethat the new surface treatment is much more effective and permanent thanthat of surface treatment without prior chemical treatment. Moreover, itwas unexpectedly discovered that the prior chemical treatment of thepowders allowed subsequent atmospheric plasma treatment of the powdersdespite their large surface area.

[0041] The present invention surface treats fluoropolymer powders byfirst contacting the powders with macromolecule chemical species whichcan be dissolved in a solvent, including water. The chemical species ismixed together with the fluoropolymer powder so that an intimate mixtureis obtained. The mixing can be accomplished in any suitable stirredvessel such as a PK blender. In addition, as discussed below, across-linking agent can be included as discussed below.

[0042] After mixing, the resulting product is subject to a heatingprocess that removes the solvent and leaves a dry macromolecule which isuniformly distributed and closely held on the surface of thefluoropolymer powder particles. The concentration of the macromoleculechemical species is from about 0.1 to about 25 wt. %, with aconcentration of from about 0.2 to about 5 wt. % being generally usefulfor purposes of the present invention. Higher surface area polymerpowders will require more of the macromolecule chemical species thanlower surface area polymer powders. Concentrations can also varydepending on the molecular weight of the macromolecule chemical species.

[0043] Macromolecules having repetitive units are particularly usefulfor purposes of the present invention. Polyvinyl alcohol, poly vinylpyrrilidone, polyethylene glycol and poly acrylic acid are non-limitingexamples of such macromolecules that provide significant functionalityper molecule.

[0044] It has been found that it is more effective to add a poly acrylicacid than add its monomer in the atmospheric plasma treatment since thedensity at which the molecule is attached to the surface of polymerpowder particles is dependent upon both the concentration of themolecule on the surface of the powder and the density of the ionized,reaction-inducing species in the plasma. Moreover, it is impossible toobtain the concentration of the monomer on the surface of the powderparticles equivalent to that obtained using the macromolecules and thepre-blending techniques. It is presumed that the ionized species causethe reaction of the macromolecule with itself, with a gradient oflinking that is positive from the particle surface to the outer surface,while the use of a cross-linking agent produces a profile that is theopposite or flat. A decrease in the molecular weight of themacromolecule, has been observed which is consistent with the fact thatthe ionized species in the plasma are effective in bringing aboutchemical reaction and even chain scission of the macromolecule. Themacromolecule develops a strong physical interaction with thefluoropolymer powder particle surface, which surprisingly becomesirreversible (they no longer can be dissolved in polar solvents) afterthe cross-linking. Thus, functionality can be effectively attached tothe powder particle surfaces without resorting to massive ion densitiesand/or long residence times in the plasma.

[0045] By titrating both alcohol and acid functions of the surfacetreated fluoropolymer powder particles the present inventor hasconcluded that the degree of surface treatment is in agreement withtheoretical calculations. It is assumed that these chemical species canreact with other species and thus improve the incorporation and resultin better blends and physical properties. This assumption has beenproven true experimentally by comparing both the uniformity offluoroelastomer/micropowder as compared to non-surface treatedequivalents by increases in the uniformity and hardness of thecomparative films produced, the increase in mixing temperatures and thephysical properties of the final product.

[0046] Subsequent extraction tests have shown that the percentage of themacromolecule chemical species attached to the surface of thefluoropolymer powder particles varies from about 40 to about 100 wt. %and is: inversely proportional to the concentration of themacromolecule, i.e. lower concentrations are more fixed; dependent onthe macromolecule and fluoropolymer species; dependent on the residencetime in the plasma and the type of gas/gas mixture of the plasma; andproportional to the power density of the plasma. This is also valid formacromolecule cross-linking.

[0047] The plasma gases, gas mixtures and macromolecular chemicalspecies all affect the chemistry of the surface treatment. In oneexample according to the present invention, when oxygen was added to aPTFE powder during treatment with PVOH, the acidity of the sample wasraised by a factor of three (caused by oxidation of the alcohol to anacid) as compared to a similar non-oxygenated treatment process.

[0048] Tests were conducted in which non-pretreated fluoropolymerpowders were subject to atmospheric plasma treatment during whichammonia and low molecular weight reactive gases were added. The resultsof these tests showed that there was a poor concentration of the reactedspecies from the reactive gas addition on the surfaces of the polymerpowder particles. These tests indicate that addition of small molecularchemical species during the atmospheric plasma treatment was ineffectivefor surface treating the fluoropolymer powders.

[0049] It was concluded that the addition of the macromolecular chemicalspecies does not necessarily have to be done using pre-solvent mixingfollowed by solvent removal by heat. Alternatively, concurrent additionof a solvent solution incorporating the macromolecule chemical speciesjust prior to, or contemporaneously with, the atmospheric plasmatreatment is foreseeable according to the present invention. Accordingto a further embodiment, the macromolecules could be provided in aliquid form without a solvent and applied directly to the fluoropolymerpowders.

[0050] In order to test the wettability of surface treated fluoropolymerpowders produced according to the present invention, samples were madeby pretreating PTFE with PVOH and subjecting the resulting pretreatedpolymer powder to atmospheric plasma treating. Up to 50 wt. % of thesurface treated PTFE was mixed with water and agitated in a pressuremill to produce a consistent paste that was found to be storage stableor could be easily resuspended by simple mixing. In other formulations,40 wt. % of the surface treated PTFE powder was mixed with water to forma paste. It was found that these pastes can be easily incorporated intoother systems without the use of surfactants or other wetting agents.

[0051] In comparative tests, it was found that untreated PTFE powder wasso hydrophobic that it could not be mixed with water without theaddition of surfactants, typically concentrations of from about 1 toabout 7 wt. % are needed.

[0052] Using the techniques of the present invention, pastes were madefrom surface treated powders of PTFE (micropowders), virgin PTFE, FEPand PVDF. These pastes were sprayed onto aluminum panels (with orwithout dilution), and the residual water was flashed off at 200° F. Thecoatings on the panels were then cured at temperatures above the meltingpoint of the fluoropolymer powders.

[0053] When curing was finished, the surface treated polymer pastesdemonstrated excellent adhesion in all cases to the aluminum panels(untreated PTFE powders are not water suspendable without a surfactantaid and even with a surfactant may not form cohesive films). Mudcrack-free films of various thicknesses from 0.03 to about 1 mils wereproduced. All the films were uniform and had good gloss characteristics.Both the surface treated FEP, ECTFE and PVDF films demonstrated verygood physical properties.

[0054] Surface treated PVDF gave a much better MEK rub resistance ascompared to untreated PVDF powder suspended with the use of asurfactant, and did not crack when subject to boiling water over a 0bend. The MEK rub resistance referred to is a standard solventresistance test which involves rubbing a surface coated with a clothsoaked in methyl ethyl ketone, and measuring the number of double fingerrubs (a double rub is one forward and one reverse rub) to rub throughthe film.

[0055] When surface treated PTFE micropowder was added to Ausimont'sfluoroelastomer TN latex it showed excellent incorporation as comparedto non-treated PTFE and when sprayed and cured at 805° F. produced atough, strong film. Similar surface treated fluoropolymer powder coatingapplied to glass panel demonstrated excellent adhesion.

[0056] The aqueous pastes produced by mixing the surface treatedfluoropolymer powders in water demonstrate novel properties.

[0057] In a surfactant suspended fluoropolymer powder system, thesurfactant is not “locked” to the polymer powder particles. Rather, itequilibrates between the aqueous phase, the particles and otherhydrophobic surfaces. This usually results in detrimental performance.For example, in surface coating applications, achievable adhesion willbe reduced caused by the surfactant equilibrating between the water,polymer and surface to be coated, resulting in a barrier to adhesion.

[0058] Also in surfactant suspended fluoropolymer powder systems, thesurfactant “holds” water up to relatively high temperatures and thus canincrease mud cracking as the coating system dries.

[0059] In polymerized aqueous dispersions of PTFE there is normallypresent a fluorosurfactant (APFO), which when used in conjunction with anormal surfactant such as Triton X-100 forms a stable dispersion. In thesurface treated fluoropolymer powder aqueous paste compositions of thepresent invention, hydrocarbon and APFO surfactants are completelyabsent. This is significant when considering that APFO is a knownbio-accumulator and its role in coating systems is usually detrimental.

[0060] In contrast to typical surfactants, the surface treatedfluoropolymer powders of the present invention have completelyhydrophilic molecules attached thereto capable of maintaining a stablepowder particle dispersion. And yet the hydrophilic molecules behave ina similar manner to surfactants, but they are immobilized (cannotmigrate) and they are surprisingly effective in providing stabledispersion at a concentration that, percent wise to the fluoropolymer,is much lower in respect to latexes of the art.

[0061] The molecules used in the surface treated fluoropolymer powderaqueous paste compositions of the present invention are “environmentallyfriendly.”

[0062] During the course of the present invention it has been it hasbeen found that the amount of the macromolecular chemical speciesrequired to make PTFE powder sufficiently wettable so that it can beused to form a uniform paste is approximated for polyethylene glycol as:Particle Diameter (microns) 0.2 1 5 30 100 Surface Area/gram (m²/g) 15 30.6 0.1 0.003 PEG/PTFE (wt. %) 11.5 2.3 0.5 0.1 0.02

[0063] Different surface treated fluoropolymer powder aqueous pastecompositions produced according to the present invention can be mixed toobtain improved and unexpected results. For example, adding FEP to a lowmolecular weight micropowder enhances the physical strength of theresulting film.

[0064] This invention provides, through a novel combination of processsteps already available in the art, a new product represented by powdersof various fluoropolymers surface treated along the present invention,which falls in-between the fluoropolymer powders and fluoropolymerlatexes of the art and, because of advantages in respect to each, iscapable of polarizing the existing application technologies towards thisnew third way of making fluoropolymers more compatible with effectiveand environmental friendly mean of application.

[0065] According to an alternative embodiment of the present invention,immobilization of the macromolecular chemical species can beaccomplished by the use of a cross-linking agent, such as, for example,an organic peroxide, that can be combined with the macromolecularchemical species prior to (or during) the coating of the fluoropolymerpowder particles. Thereafter, the coated fluoropolymer powder particlescan be heated to effect cross-linking of the macromolecules (bydecomposition of the cross-linking agent into reactive species) withoutsubsequent atmospheric plasma treatment (which can still be optionallyused).

[0066] The following non-limiting Examples illustrate various featuresand characteristics of the present invention which are not to beconstrued as limited thereto. Throughout the Examples and elsewhereherein percentages are by weight unless otherwise indicated.

EXAMPLE 1 Surface Treatment of Powders

[0067] In this Example fluoropolymer powder particles were surfacetreated with a number of macromolecular chemical species.

[0068] Table 1 lists the fluoropolymer powders, their average particlesize and molecular weight. Table 2 lists the macromolecular chemicalspecies, their molecular weights, minimum and maximum concentrations,cross linking-agents and concentrations of the cross-linking agents.TABLE 1 Average Particle Base Powder Size. D₅₀ Microns Molecular WeightPTFE 35 >1 × 10⁶ Irradiated PTFE 3 to 15 1 × 10³-1 × 10⁶ PVDF  5 MeltViscosity 30 Kp @ 232° C. FEP 5 to 25 Melt Index 2 to 20 @ 375° C. ECTFE25 Melt Index 12

[0069] TABLE 2 Min Typical conc. Typical Conc. Max Conc. Cross-cross-linking Macromo- Commercial Molecular gm/gm of gm/gm of linkingagent gm/gm of lecular Name weight powder powder agent macromolecule PEG300, 0.003 0.1 Polycup 0.1 900 and 172 1450 PVOH Celvol 15,000 0.0010.05 Polycup 0.1 502 172 PAA 90,000 0.003 0.05 Diak #3 0.05 EpoxyCoatasil 288 0.02 0.02 Hydrolysis 0 Functional 1770 Silane NonSilquest >300 0.02 0.02 Hydrolysis 0 Ionic 1230 Silane PVP PlasdoneUnknown 0.02 0.02 None 0 C-15

[0070] To surface coat the fluoropolymer powder particles, a measuredamount of the fluoropolymer powder (typically 2 Kg) was charged into acommercial solid/liquid blender. The blender was then started and adesired amount of the macromolecular chemical species (typically 10 gm)and a desired amount of cross-linking agent (typically 0.25 gm) wasadded to the blender and the blending blades were started. The mixturewas blended for about 15 minutes. After mixing, the material was placedon a tray and dried in a 104° C. oven for about 2 hours. Evaporation ofwas determined by measuring weight loss. After drying, the driedmaterial was heated in a 150° C. oven to activate the cross-linkingagent.

[0071] The surface coated fluoropolymer powders were subject toatmospheric plasma treatment by passing the powders through a plasmaalong a vibrating trough. A treatment apparatus was set up whichincluded a vibrating trough, plasma electrodes, a readily ionizable gassupply, an optional reactive gas supply, and cooling systems for theelectrodes and the vibrating trough (to transport the fluoropolymerpowders through the plasma). An air flow was initiated to cool theelectrodes and water was used to cool the vibrating trough. A flow ofionizable gas (e.g. 2990 ml/min Helium) was provided together with anoptional reactive gas, when used (e.g. 300 ml/min oxygen). Theelectrical power to the electrodes was adjusted to about 1.5 kilowattsto create a plasma. The vibrating trough was adjusted to transport about0.25 kg/min of the fluoropolymer through the plasma. The fluoropolymerpowder can be repeatedly passed though the plasma a number of times toobtain desired properties. A similar APT process is used forfluoropolymer powders that are either pretreated (coated) or notpretreated with a macromolecular chemical species.

EXAMPLE 2 Hydroxyl and Acid Numbers

[0072] Titrating both alcohol and acid functions of the surface treatedfluoropolymer powder particles can be used to determine the degree ofsurface treatment.

[0073] In this Example the method of ASTM D 1957-86 was followed. Thismethod utilizes acetylation reaction, which converts the primary alcoholto an ester through reaction with acetic anhydrate, liberating one moleof acetic acid. Upon hydrolysis, the same will require less potassiumhydroxide to reach the phenolphthalein end point (neutralization)relative to a control, which upon hydrolysis yields 2 moles of aceticacid.

[0074] In this Example, 10.0 g of each individual surface treated powderwas placed in a 250 ml Erlenmeyer flask and the total weight of thesample and flask were recorded. 5 ml of 3:1 volume mixture of pyridine:acetic anhydride were added to the flask.

[0075] 9.0-11.0 g of the same sample was placed in a second flask foracid value titration and the total weight of the sample and flask wasrecorded. 10 ml pyridine was added to the second flask.

[0076] Both flasks were provided with refluxing condensers and thecontents were stirred and heated to 100° F. for one hour. After heating10 ml of water was added to each flask and the contents were allowed tocool for 10 minutes.

[0077] After cooling, 25 ml butyl alcohol was added to each flaskthrough the refluxing condensers. Then 1 ml phenolphthalein was added toeach flask and neutralized with 0.5 N potassium hydroxide in ethanolsolution.

[0078] The hydroxyl value was calculated by the equation:

Hydroxyl value=B+(SA/C)−V/S×N(56.1)

[0079] where A=KOH solution required for titration of the acid value inml; B=KOH solution required for titration of the reagent blank in ml;C=sample used for the acid value in grams; V=KOH solution required fortitration of the acetylated specimen in ml; and S=sample for acetylationin grams; and N=normality (0.5).

[0080] Typical hydroxyl and acid numbers for several samples of surfacetreated fluoropolymer powders are give in Table 3. TABLE 3 Concen-Number tration on passes Acidity Macro- the Polymer through (mgs)Hydroxyl Polymer molecular (wt. %) APT KOH/gm Value Higher mo- None 0 00.3 — lecular wt. micropowder PTFE None 0 0 0.9 — micropowder PTFE PEG900 5.0 2 1.2 — micropowder PTFE PEG 900 5.0 4 1.4 — micropowder PTFEPEG 900 5.0 6 1.7  2.9 micropowder PTFE PAA 2.0 6 13.2 — micropowderPTFE PVOH 2.0 0 0.3 21.0 micropowder PTFE PVOH 2.0 2 0.8 16.4micropowder PTFE PVOH 2.0 6 0.6 16.7 micropowder

[0081] The results of this Example were used to verify that the degreeof surface treatment achieved in practice is in general agreement withtheoretical calculations.

EXAMPLE 3 Weight Loss and Extraction Results

[0082] In this Example extraction tests were performed to determine theamount of surface treated material which is neither covalently attachednor permanently adsorbed one the fluoropolymer powder.

[0083] About 5 g of each sample was placed on an analytical balanced andthe weight was recorded. 60 ml of an appropriate solvent (isopropanolfor polyethylene glycol, deionized water for polyvinyl alcohol, etc.)was mixed with the sample. The mixture was mixed for 2 hours over lowheat (about 100° F.). After heating the sample mixture was poured into a150 ml Durapore™ 0.22 μm filtration device. The material that wasremoved as the solvent passes through the filter and was collected. Thetotal weight of the solvent (containing the extracted material) wasrecorded. About 1 g of the solvent was placed into a aluminum weightingdish and the total weight of the solvent and dish are weighed. Thesolvent was evaporated in a vented oven that was heated to 100° C. Thepercentage of material extracted was calculated by the equation:

E=100×[(F−P)/S]×T/W

[0084] where E=percentage of surface treatment extracted; F=final weightof pan and extracted material after evaporation; P=tare pan weight;S=sample weight of solvent for percent solids test; T=total weight ofsolvent; W=weight of fluoropolymer sample.

[0085] The procedure of this Example was used to produce the graph ofFIG. 1 which shows weight loss versus number of passes throughatmospheric plasma treatment for 5% PEG on PTFE. The graph includes acomparison between actual measured values versus predicted weight loss.In FIG. 1, weight loss was measured at 200° C. for 2 hours. Extractionwas achieved by washing the polymer with excess water.

[0086] FIG. 1 shows that the amount of PEG attached to the polymer (andnot removed by evaporation or extraction) increases as treated PTEF isrepetitively passed through the APT. Since the hydroxyl values do notfollow the empirical predicted weight loss in FIG. 1 which show adownward trend with APT it can be concluded that the PEG was not beingevaporated.

EXAMPLE 4 Spray Test Results

[0087] In this Example surface treated fluoropolymer powders were formedinto pastes that were sprayed onto aluminum panels to test coatingproperties.

[0088] Pastes having 40 wt. % solids were prepared by placing a desiredamount of deionized water into a mixing bowl and creating a vortex.Next, enough fluoropolymer powder was introduced directly into thevortex to produce a mixture having 40 wt. % solids. The mixing wascontinued until the mixture was homogeneous and then the mixture waspassed through a horizontal mill.

[0089] The powder pastes were sprayed onto aluminum Q-panels using anair assisted Binks Model 69 spray gun with a #66S fluid nozzle and #66SDair cap. Additional water can be used if necessary for ease of sprayingas determined by the operator. After spray coating the panel were thenflashed to remove water in a well-ventilated oven for 2 minutes at 100°C. The coated panels were then cured for approximately 10 minutes at atemperature of about 30° C. above the melting point of thefluoropolymer.

[0090] The thickness of the films was in the range of 0.1-1.0 mil (dryfilm thickness). The films were rated according to critical crackingthickness, film integrity, flexibility and overall appearance, includinggloss, color, etc.

[0091] Data and analysis of several coatings are presented in Table 4.TABLE 4 Macro- Cure Polymer molecule Temp Thickness Film Quality PTFENone N/A Cannot disperse PTFE in micropowder water without surfactant.PTFE None 805 0.25 Some mud cracking. micropowder 1% Triton X Good film,average adhesion, poor physicals. PTFE 0.5% PVOH 805 0.85 No mudcracking. Good micropowder film. Good adhesion, poor physicals. PTFE 2%PAA 805 0.3 No mud cracking. Good micropowder gloss, Clear. Goodadhesion, poor physicals. PTFE 2% PAA + 805 0.15 No mud cracking. Goodmicropowder PEG gloss. Good adhesion, poor physicals. PTFE 5% PEG 8050.5 No mud cracking. Good micropowder gloss. Some browning. Goodadhesion, poor physicals. FEP 0.5% PVOH 750 0.1 Very good adhesion. Verygood gloss. Tough coating. PVDF None 1% 550 0.1 Poor adhesion. VeryTriton X good gloss. Tough coating. Poor resistance to MEK rub and poorbend test performance. PVDF 0.5% PVOH 550 0.1 Very clear. Very goodadhesion. Decent gloss. Tough coating

[0092] The results shown in Table 4 indicate that the surface treatedfluoropolymer polymer powders produced according to the presentinvention can be used to produce fluoropolymer surface coatingsaccording to relatively simple and efficient spray processes.

[0093] The surface treated polyfluoropolymers powders of the presentinvention can be used to produce various articles, compositions andadditives. Several exemplary examples include fillers, extrusion aids,additives in oils, greases and other lubricants, and additives in andinks, paints and coating compositions.

[0094] In addition to atmospheric plasma treatment, during the course ofthe present invention, it was also determined that other process such asx-ray radiation, electron radiation, and ultraviolet radiation, could beused to immobilize the macromolecules on the surfaces of thefluoropolymer powders by effecting cross-linking.

[0095] Although the present invention has been described with referenceto particular means, materials and embodiments, from the foregoingdescription, one skilled in the art can easily ascertain the essentialcharacteristics of the present invention and various changes andmodifications can be made to adapt the various uses and characteristicswithout departing from the spirit and scope of the present invention asdescribed above.

What is claimed is:
 1. A surface treated fluoropolymer powder whichcomprises: powder particles of a fluoropolymer; and a coating ofmacromolecules on individual ones of said powder particles.
 2. A surfacetreated fluoropolymer powder according to claim 1, wherein the coatingof macromolecules comprises macromolecules which are cross-linked to oneanother.
 3. A surface treated fluoropolymer powder according to claim 2,wherein the cross-linked macromolecules are cross-linked by atmosphericplasma treatment.
 4. A surface treated fluoropolymer powder according toclaim 2, wherein the macromolecules comprise repetitive units.
 5. Asurface treated fluoropolymer powder according to claim 4, wherein themacromolecules comprise at least one of polyvinyl alcohol, polyvinylpyrrilidone, polyethylene glycol, poly acrylic acid and mixturesthereof.
 6. A surface treated fluoropolymer powder according to claim 1,wherein the fluoropolymer powder particles are produced bypolymerization of at least one of the following fluoromonomers:tetrafluoroethylene, vinylidene fluoride, hexafluoropropylene, vinylfluoride, trifluoroethylene and chlorotrifluoroethylene.
 7. A surfacetreated fluoropolymer powder according to claim 6, wherein thefluoropolymer powder particles comprise at least one of the followingpolymers: polytetrafluoroethylene, polychlorotrifluoroethylene,polyvinylidene fluoride, polyvinylfluororide; or the followingcopolymers: tetrafluoroethylene-hexafluoropropylene,tetrafluoroethylene-perfluorovinylether, tetrafluoroethylene-ethylene,hexafluoroethylene-vinylidene fluoride, tetrafluoroethylene-ethylene,ethylene-chlorotrifluoroethylene; or terpolymers of:tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride, or mixturesthereof.
 8. A surface treated fluoropolymer powder according to claim 1,wherein the fluoropolymer powder particles have a particle size of lessthan about 100 microns.
 9. A surface treated fluoropolymer powderaccording to claim 1, wherein the coating of macromolecules comprisesmacromolecules which are covalently bonded to surfaces of thefluoropolymer powder particles.
 10. A substrate coated with the surfacetreated fluoropolymer powder of claim
 1. 11. An article of manufacturemade from the surface treated fluoropolymer powder of claim
 1. 12. Amethod of providing a modified surface characteristic to fluoropolymerpowder particles which comprises the steps of: a) providing afluoropolymer powder; b) contacting the fluoropolymer powder with amacromolecular chemical species to coat particles of the fluoropolymerpowder with macromolecules; and c) subjecting the coated particles fromstep b) to a process that immobilizes the macromolecules on the surfaceof the powder particles.
 13. A method of providing a modified surfacecharacteristic to fluoropolymer powder particles according to claim 12,wherein the process to which the coating particles are subject to instep c) comprises at least one of atmospheric plasma treatment, x-rayradiation, electron radiation, ultraviolet radiation, and heating.
 14. Amethod of providing a modified surface characteristic to fluoropolymerpowder particles according to claim 12, wherein the macromolecules areimmobilized in step c) by cross-linking the macromolecules.
 15. A methodof providing a modified surface characteristic to fluoropolymer powderparticles according to claim 12, wherein the macromolecules compriserepetitive units.
 16. A method of providing a modified surfacecharacteristic to fluoropolymer powder particles according to claim 12,wherein the macromolecules comprise at least one of polyvinyl alcohol,polyvinyl pyrrilidone, polyethylene glycol, poly acrylic acid,copolymers thereof, and mixtures thereof.
 17. A method of providing amodified surface characteristic to fluoropolymer powder particlesaccording to claim 12, wherein the fluoropolymer powder particles areproduced by polymerization of at least one of the followingfluoromonomers: tetrafluoroethylene, vinylidene fluoride,hexafluoropropylene, vinyl fluoride, trifluoroethylene andchlorotrifluoroethylene.
 18. A method of providing a modified surfacecharacteristic to fluoropolymer powder particles according to claim 17,wherein the fluoropolymer powder particles comprise at least one of thefollowing polymers: polytetrafluoroethylene,polychlorotrifluoroethylene, polyvinylidene fluoride,polyvinylfluororide; or the following copolymers:tetrafluoroethylene-hexafluoropropylene,tetrafluoroethylene-perfluorovinylether, tetrafluoroethylene-ethylene,hexafluoroethylene-vinylidene fluoride, tetrafluoroethylene-ethylene,ethylene-chlorotrifluoroethylene; or terpolymers of:tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride, or mixturesthereof.
 19. A method of providing a modified surface characteristic tofluoropolymer powder particles according to claim 12, wherein thefluoropolymer powder particles have a particle size of less than about100 microns.
 20. A substrate coated with a surface treated fluoropolymerpowder produced according to the method of claim
 12. 21. A method ofcoating a substrate with a fluoropolymer material which comprises thesteps of: a) providing a fluoropolymer powder; b) contacting thefluoropolymer powder with a macromolecular chemical species to coatparticles of the fluoropolymer powder with macromolecules; c) subjectingthe coated particles from step b) to a process that immobilizes themacromolecules on the surface of the powder particles; and d) applyingthe surface treated particles to the surface of a substrate.
 22. Amethod of coating a substrate with a fluoropolymer material according toclaim 21, wherein the process to which the coated particles are subjectto in step c) comprises at least one of atmospheric plasma treatment,x-ray radiation, electron radiation, ultraviolet radiation, and heating.23. A method of coating a substrate with a fluoropolymer materialaccording to claim 21, wherein the macromolecules are immobilized instep c) by cross-linking the macromolecules.
 24. A method of coating asubstrate with a fluoropolymer material according to claim 21, whereinthe macromolecules comprise repetitive units.
 25. A method of coating asubstrate with a fluoropolymer material according to claim 21, whereinthe macromolecules comprise at least one of polyvinyl alcohol, polyvinylpyrrilidone, polyethylene glycol, poly acrylic acid, copolymers thereof,and mixtures thereof.
 26. A method of coating a substrate with afluoropolymer material according to claim 21, wherein the fluoropolymerpowder particles are produced by polymerization of at least one of thefollowing fluoromonomers: tetrafluoroethylene, vinylidene fluoride,hexafluoropropylene, vinyl fluoride, trifluoroethylene andchlorotrifluoroethylene.
 27. A method of coating a substrate with afluoropolymer material according to claim 21, wherein the fluoropolymerpowder particles comprise at least one of: the following polymers:polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidenefluoride, polyvinylfluororide; or the following copolymers:tetrafluoroethylene-hexafluoropropylene,tetrafluoroethylene-perfluorovinylether, tetrafluoroethylene-ethylene,hexafluoroethylene-vinylidene fluoride, tetrafluoroethylene-ethylene,ethylene-chlorotrifluoroethylene; or terpolymers of:tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride, or mixturesthereof.
 28. A method of coating a substrate with a fluoropolymermaterial according to claim 21, wherein the fluoropolymer powderparticles have a particle size of less than about 100 microns.
 29. Amethod of coating a substrate with a fluoropolymer material according toclaim 21, wherein the surface treated particles are applied to thesurface of the substrate by one of spraying, brushing and dipping.
 30. Amethod of coating a substrate with a fluoropolymer material according toclaim 21, wherein after being applied to the surface of the substratethe surface treated particles are heated above their melting point. 31.A dispersion comprising a surface treated fluoropolymer powder in apolar solvent.
 32. A dispersion according to claim 31, wherein thesurface treatment fluoropolymer powder includes powder particles thathave macromolecules immobilized thereon which present polar groups thatreact with polar groups in the polar solvent.
 33. A dispersion accordingto claim 31, wherein the dispersion comprises a slurry.
 34. A dispersionaccording to claim 31, wherein the dispersion comprises a paste.
 35. Asurface treated inert polymer powder which comprises: powder particlesof an inert polymer; and a coating of macromolecules on individual onesof said powder particles.
 36. A surface treated inert polymer accordingto claim 35, wherein the inert polymer comprises at least one ofpolyether ether and polyetherimide.
 37. A method of providing a modifiedsurface characteristic to inert polymer powder particles which comprisesthe steps of: a) providing an inert polymer powder; b) contacting theinert polymer powder with a macromolecular chemical species to coatparticles of the inert polymer powder with macromolecules; and c)subjecting the coated particles from step b) to a process thatimmobilizes the macromolecules on the surface of the powder particles.38. A method of providing a modified surface characteristic to inertpolymer powder particles according to claim 37, wherein the process towhich the coated particles are subject to in step c) comprises at leastone of atmospheric plasma treatment, x-ray radiation, electronradiation, ultraviolet radiation, and heating.
 39. A method of providinga modified surface characteristic to inert polymer powder particlesaccording to claim 37, wherein the inert polymer comprises at least oneof polyether ether and polyetherimide.